The parotid glands of rats have been shown to be profoundly affected by increased or decreased mastication of food. With reduced mastication (a liquid diet), there is gland atrophy. With enhanced mastication (a bulk diet), there is gland enlargement. We have investigated the effects of enhanced and reduced mastication on the protein composition of parotid saliva. When gland enlargement is stimulated by increased mastication of food, there are parallel increases in the saliva concentration of protein and of three secretory enzymes (amylase, RNase and DNase). Electrophoretic profiles in anionic, cationic and SDS acrylamide gels show no additions or deletions of bands and no major differences in the quantity of stained material in each band. In contrast, there are striking alterations in the protein composition of the parotid saliva of rats fed a liquid diet. There are non-parallel decreases in the three enzymes and in protein. Cationic and SDS acrylamide gels indicate that three major proteins are absent. We will isolate from the saliva of control animals the proteins that are missing in the saliva of rats fed the liquid diet. We will determine several biochemical properties of these proteins, their molecular weight, their amino acid composition and their isoelectric points. These proteins are currently of special interest because of their unusual composition. They are basic proline-rich proteins and three acids--proline, glycine and glutamic acid/glutamine--comprise more than 75% of their total amino acid residues. Preliminary findings indicate that certain acidic proline-rich proteins are also affected when mastication is reduced. We will devise procedures to isolate and identify these proteins and to then determine the manner in which they are affected by altered mastication.